Sleep disturbances are common among older persons. Exposure to synchronizing agents for athe circadian system (zeitgebers) such as bright light, social cues and physical activity are greatly diminished in old age. This is particularly true for the institutionalized elderly and may contribute to the constellation of sleep/wake cycle and behavioral disorders which are frequently seen in this group. Preliminary studies indicate that enforcement of photic and non-photic zeitgebers results in alterations of circadian rhythmicity and sleep with associated improvements in daytime function in elderly residents of assisted facilities. The specific aims of the present project are: 1) To test the hypothesis that the timing of bright light/dark or social/physical activity schedules is critical to their efficacy to alter circadian rhythms and sleep, as well as to improve daytime alertness and performance, 2) To test the hypothesis that enforcement of a social schedule without a concomitant increase in physical activity will improve daytime function and nocturnal sleep, and 3) To test the hypothesis that reinforcement of sleep homeostatic mechanisms by enhancement of slow wave sleep will increase alertness and measures of performance. Older residents of assisted living and retirement facilities will be studies before, during and after a 14 day period of intervention will either morning or evening bright light, or structured social and physical exercise; social activity alone or combined social and physical activity programs; or pharmacological treatment to enhance slow wave sleep. Rest-activity cycles and light exposure will be monitored continuously throughout each protocol. Circadian profiles of temperature and heart rate, tests of neuropsychological performance, recording of nocturnal sleep, and measurement of melatonin and cortisol levels in saliva will be determined before, during and after athe various treatments. The results from these studies will determine the extent to which photic and non-photic zeitgebers can be used to alter circadian rhythmicity, improve sleep, alertness and performance in the elderly, as well as to provide essential practical information for th application of these types of intervention in the "real world" setting.